John Adolphus of Schleswig-Holstein-Sonderburg-Plön (German: Johann Adolf or Hans Adolf; 8 April 1634, Ahrensbök – 2 July 1704 Ruhleben) was the second Duke of Schleswig-Holstein-Sonderburg-Plön, which had been created by a division of the Duchy of Schleswig-Holstein-Sonderburg.

He was born on 8 April 1634 in Ahrensbök, the eldest son of the first Duke of Plön, Joachim Ernest and Dorothea Augusta of Schleswig-Holstein-Gottorp.

From 1645 to 1650 he went on a grand tour around the countries of Europe, including England and France.

John Adolphus took part in several of the major wars of his time, including the Ottoman wars and handed over the running of his duchy during those times largely to his mother and his wife.

In 1704 went to Hungary and fought against the Kurucs with the forces of Holstein-Plön and Denmark.